With an increase in the adoption of wireless communication standards in small handheld devices such as cellular phones, the amount of self-generated interference in those devices increases. The various communication interfaces are often required to coexist. Harmonic reject (HR) mixers may help mitigate coexistence issues, but harmonic rejection properties of HR mixers greatly depend on the accuracy of the phase difference between local oscillator (LO) waveforms.
Switching mixers with rejection properties on one or more odd higher harmonics are well known, see, e.g., J. A. Weldon et al., “A 1.75-GHz highly integrated narrow-band CMOS transmitter with harmonic-rejection mixers”, IEEE Journal of Solid-State Circuits, Vol. 36, No. 12, December 2001, pp 2003-2015. A harmonic-rejection (HR) mixer allows simplifying the RF filtering. A typical HR mixer known in this field is an active (Gilbert) type of mixer. However, passive mixers are known to provide a better 1/f noise and higher linearity. On the other hand, a passive HR mixer is more difficult to implement.
HR mixers are also disclosed in non pre-published European patent application 072 90 983.1, filed Aug. 7, 2007 for “Harmonic Rejection Mixer Unit and Method for Performing a Harmonic Rejection Mixing” (attorney docket PH 008194).
Reference is also made to A. Y. Valero Lopez, S. T. Moon, E. Sánchez-Sinencio, “Self-Calibrated Quadrature Generator for WLAN Multistandard Frequency Synthesizer”, IEEE J. of Solid State Circuits., May 2006, vol. 41, no 5, pp. 1031-1041.